The invention relates to the field of synthetic aperture arrays and more specifically to the field of optical synthetic aperture arrays.
High resolution projection systems are used to project an image of a mask onto the surface of a semiconductor wafer coated with a chemical photoresist during the fabrication of semiconductor circuits. Exposed regions of photoresist within the image of the mask are chemically altered and react differently to subsequent chemical or physical treatment of the wafer than unexposed regions. A series of masks and intervening treatments are used to form layers on the wafer having the required electronic structures.
The masks used in the process are expensive and time consuming to produce. Further changes required in the circuitry after the mask is produced typically require a new mask to be created. The complex optical systems used in the process are also expensive and require significant maintenance. High numerical aperture lenses have small depths of field and are limited in contrast at higher spatial frequencies. The demanding requirements of the semiconductor industry for higher resolution, contrast, depth of field and optical efficiency are coupled with a desire to minimize distortion. Physical constraints inherent in projection lens systems will limit further performance improvements.
The present invention overcomes the problems associated with the use of physical masks and lenses.
The invention relates to a synthetic aperture system for producing a non-periodic pattern in a region of overlap. The system includes a source of electromagnetic radiation producing a plurality of electromagnetic beams, a plurality of beam controllers positioned to receive a respective one of the plurality of electromagnetic beams and direct the respective electromagnetic beam into the region of overlap and a system controller in electrical communication with each of the plurality of the beam controllers. Each beam controller controls at least one of the phase, amplitude and polarization of a respective one of the plurality of electromagnetic beams in response to control signals from the system controller. The result is a non-periodic pattern formed within the region of overlap by the interference of a plurality of electromagnetic beams in response to the control signals from the system controller.
In one embodiment the plurality of sources of electromagnetic radiation includes a laser producing an electromagnetic beam and a beam splitter device positioned to receive the electromagnetic beam and produce a plurality of electromagnetic sources therefrom. In one embodiment one of the beam controllers includes an acousto-optic modulator.
In another embodiment the system includes a field stop adjacent to the image plane. The field stop limits a spatial extent of the non-periodic pattern. In still yet another embodiment the system further includes an apodizing element for at least one of the plurality of electromagnetic beams. The apodizing element limits a spatial extent of the at least one electromagnetic beam.
The invention also relates to a method for producing a non-periodic pattern in a region of overlap. The method includes the steps of providing a plurality of electromagnetic beams, directing the plurality of electromagnetic beams into the region of overlap, and modulating at least one of the phase, amplitude and polarization of at least one of the plurality of electromagnetic beams to thereby form a predetermined non-periodic pattern on the image plane by the interference of the plurality of electromagnetic beams.
In one embodiment the step of modulating at least one of the phase, amplitude and polarization of each of the plurality of electromagnetic beams includes the steps of providing an acoustic-optic modulator and acoustic-optically modulating the electromagnetic beam. In another embodiment the step of providing the plurality of electromagnetic beams includes the steps of providing a source of an electromagnetic beam and splitting the electromagnetic beam into a plurality of electromagnetic beams.
In another embodiment the method further includes the steps of providing a substrate, providing a layer of photoresist on the substrate, and exposing the photoresist to the non-periodic pattern. In yet another embodiment the method further includes repeating the step of modulating to generate a predetermined pattern in the layer of photoresist. In still another embodiment the method further includes the step of calibrating the interference pattern prior to forming the non-periodic pattern. In one embodiment the step of calibrating the interference occurs during the generation of the non-periodic pattern. In still yet another embodiment the method includes the step of apodizing the non-periodic pattern.
The invention also relates to a system and a method that can be used to replace the lens, the mask and the mask illuminator of conventional lithography systems with a discrete set of controllable beam sources. Highly reliable solid-state modulators can be used to control the amplitudes and phases of the beams. The system and method are scaleable to wavelength regimes for which high numerical aperture lenses are not feasible. Further advantages include the optimum use of beam energy, excellent control of contrast and a large depth of field.